Shining only ~300 million years after the Big Bang, it may be home to the oldest stars in the universe.
An international team of astronomers has recently spotted the most distant galaxy ever, located about 13.5 billion light-years away. Astronomers named this galaxy HD1, which is exceptionally bright in ultraviolet light. Astronomers think that some sort of process must have been occurring there or did occur some billions of years ago.
The team started speculating what the galaxy was. They proposed two ideas: HD1 may be forming stars at an astounding rate and may probably be the home of Population III stars, the universe’s very first stars. Also, the HD1 has a supermassive black hole about 100 million times the mass of our Sun.
Initially, astronomers assumed that HD1 was a typical starburst galaxy. But after calculating its star formation rate, they found that HD1 would form more than 100 stars every year. This is at least ten times higher than we expect for these galaxies.
Fabio Pascucci, a lead author of the MNRAS study and co-author of the discovery paper on ApJ, said, “The very first population of stars that formed in the universe were more massive, more luminous, and hotter than modern stars. If we assume the stars produced in HD1 are these first or Population III stars, their properties could be explained more easily. Population III stars can produce more UV light than normal stars, which could clarify the extreme ultraviolet luminosity of HD1.”
Its supermassive black hole could also explain its luminosity. As it gobbles down enormous amounts of gas, high-energy photons may be emitted by the region around the black hole.
Pascucci said, “If that’s the case, it would be by far the earliest supermassive black hole known to humankind, observed much closer in time to the Big Bang than the current record-holder.”
Avi Loeb, an astronomer at the Center for Astrophysics and co-author of the MNRAS study, said, “HD1 would represent a giant baby in the delivery room of the early universe. It breaks the highest quasar redshift on record by almost a factor of two, a remarkable feat.”
Astronomers discovered HD1 after more than 1,200 hours of observing time with the Subaru Telescope, VISTA Telescope, UK Infrared Telescope, and Spitzer Space Telescope.
The team used Atacama Large Millimeter/submillimeter Array (ALMA) to confirm the distance. It is 100 million light-years further than GN-z11, the current record-holder for the furthest galaxy.
Yuichi Harikane, an astronomer at the University of Tokyo who discovered the galaxy, said, “It was very hard work to find HD1 out of more than 700,000 objects. HD1’s red color matched the expected characteristics of a galaxy 13.5 billion light-years away surprisingly well, giving me some goosebumps when I found it.”
Scientists are planning to continue further observations with James Webb Space Telescope. If current calculations prove correct, HD1 will be the most distant — and oldest — galaxy ever recorded.